1. Field of the Invention
The present invention relates to a vehicle tire including a tread having a plurality of axial end sections and sipes (or slots) running substantially in an axial direction in at least one of the axial end sections when viewed from the top (i.e., perpendicular to the tread surface). As used herein, the term "sipe" refers to a void in the tread which closes up when in the footprint of the tire. The sipes are corrugated with corrugated ridges (or crests or peaks) and valleys such that the corrugated ridges and valleys are substantially straight lines and diagonally inclined in an oblique plane substantially parallel to a longitudinal extent of the sipe.
2. Discussion of Background Information
Tires similar in general to the type described above are known. The substantially axially running sipe, which may also be referred to as a transversal sipe, extends or runs, as is known in the prior art, not exactly in the axial direction but, preferably, at an angle of approximately 10.degree. to 60.degree. to the axis. When the tire tread is equipped with transversal sipes, the tread preferably is designed to run substantially parallel to the transversal sipes.
The remaining rubber between the sipes is generally referred to as a bridge. A successive arrangement of profile blocks in a circumferential direction is generally referred to as a track of segments. A successive arrangement of sipes in the circumferential direction is generally, and analogously, referred to as a track of sipes.
In principle, sipes reduce stiffness, particularly with respect to forces perpendicular to these sipes. Transversal sipes particularly reduce stiffness in the longitudinal direction.
The softening of the tread results in a tire surface that conforms more accurately to the surface roughness of the road in the contact area In this manner, a higher degree of friction with the surface is achieved.
The traction-enhancing effect is documented, e.g., particularly on snowy roads, based on the fact that a bridge bending effect, which already occurs with low longitudinal forces, causes the terminal ends of the bridges to extend into the contact area in their oblique position, thus, making contact with their edges and not in a planar manner. This formation of edges has particularly improved the traction on packed snow and on ice.
However, it has been found that the oblique positioning of the bridge ends has a negative effect on the braking path on wet roads. This disadvantage is particularly unfortunate for modem winter tires, because it is important to achieve not only good traction on snow but good braking performance on wet roads. This is further important because rainy road conditions occur more frequently than snowy conditions. Even on dry roads, a high degree of surface friction is expected of summer tires. For example, on a dry road, the oblique positioning of the ends also leads to a reduction of traction, although it still remains very high. Based on the proven winter tires, the braking performance on wet and partially dried roads was improved by reducing the number of sipes, particularly, the number of transversal sipes. However, this results in a poorer performance on snow.
French Patent No. 791 250 (issued in 1935) discloses a vehicle tire having a running tread which, when viewed from the top, exhibits substantially axially running sipes in an axial end section. The sipes have a corrugation with corrugated ridges and valleys that are straight lines and extend diagonally in an oblique plane. The diagonal direction of the corrugated ridges and valleys, with respect to a radially outward direction of the tire, extend axially outward, i.e., away from a axial tire center.
German Patent Application P 44 27 895.0 (published in 1994) discloses a vehicle tire having a tread which, when viewed from the top, exhibits substantially axially running sipes in either one or both axial end sections. The running sipes have a corrugation with corrugated ridges and valleys that are straight lines and extend diagonally in an oblique plane parallel to the running sipe. The diagonal direction of the corrugated ridges and valleys, with respect to the radially outward direction, extends axially inward, i.e., toward the axial tire center.
The two mirror-inverted embodiments disclosed in the prior art show a tendency to only use sipes that are spaced fairly close to each other for small terminal end rotations with only a small degree of resistance, and to minimize the additional enlargement of the terminal end rotations due to increasing tangential forces by interlocking the bridges with each other. However, the main effect of the prior art is that a very small end rotation is effective for improving the traction on snow and ice, but does not have a significant impact on the braking on a wet or dry road, and a larger terminal end rotation increases the traction on snow and ice only to an insignificant degree, but would decrease the braking performance on wet and dry surfaces significantly. In the German document this effect is even better utilized than in the French document.